0023912: TDataStd_ExtStringArray::Value() returns a copy of TCollection_ExtendedString, but it might return a reference.

Since now TDataStd_ExtStringArray::Value() returns a constant reference to the string value.
Also, a draw-command GetExtStringArray is modified to manipulate with the string by a constant reference.
Added test case bugs/caf/bug23912

src/TDataStd/TDataStd_ExtStringArray.cdl

@@ -64,6 +64,7 @@ is
     Value (me; Index : Integer from Standard)
     ---Purpose: Returns the value of  the  <Index>th element of the array
     --
+    ---C++: return const &
     ---C++: alias operator ()
     returns ExtendedString from TCollection;